During mining operations it is necessary to protect a variety of electrical cables, water hoses and other service lines from damage. One particular area where line protecting apparatus is required, is in the area of coal mining, particularly in longwall coal mining in which a coal cutter traverses back and forth across a coal face depositing coal cut from the coal face into a conveyor disposed behind the coal cutter. In order to operate, the coal cutter requires a supply of water and electricity, which are provided by service lies. The service lines are located in a trough which is typically disposed on the opposite side of the conveyor from the coal cutter and the lines travel up and down the trough as the coal cutter moves up and down the coal face. It should be noted however, that whilst the type of apparatus envisaged by the present invention is particularly suitable for use in handling and protecting service lines for longwall coal mining, other applications of the apparatus are possible.
In order to protect such service lines, it is known to enclose, or at least partially enclose them in a protective articulated cable handler formed from a plurality of interconnected links. U.S. Pat. No. 4,988,838 discloses one such cable handler formed from a plurality of interconnected links. Each link has a central web forming a common base for a pair of laterally open channels on respective sides of the central web. For at least some of the links, each channel is formed with a inwardly extending nib so that the entrance to the channel is narrower than the width of the channel. Each link is formed from a plastics material, typically nylon, so that the channel sides are resiliently flexible and a service line can be inserted into a respective one of the channels by deflecting walls of the channel and the nibs apart. After a service line is passed through the channel entrance, the channel sides return back to regain their original position and thus prevent the line from inadvertently moving out of the channel. The links are joined by linking the central web of one link to adjacent links hence such cable handlers are referred to as “centre pull” cable handlers. Centre pull cable handlers also preferred because the water hose is kept separate from the electric cable for safety & reliability reasons.
PCT/GB95/00384 discloses a development of the apparatus shown in U.S. Pat. No. 4,988,838 in which the web is located to one side of the link instead of being centrally located, and the channel is approximately twice the depth of the centre pull design. This type of cable handler is referred to as a “side pull” cable handler, as the links are articulated via the side web and are pulled along one side only.
One problem which is common to the cable handlers of both U.S. Pat. No. 4,988,838 and PCT/GB95/00384 results from the presence of stones, flints and the like in the trough along which the cable handler runs. These flints and stones are often narrower than the channel entrance and they can enter the channel and may puncture the water hose or electric cable, thus interrupting the supply of power or water to the coat cutter and disrupting production. Further, the type of heavy duty cables used in underground mining are expensive, particularly the electric cables. The cost of replacing any damaged cables, is high, such that in some environments, mining operators will not use cable handlers of the type described in U.S. Pat. No. 4,988,838 because of the potential for damage to the service lies.
To avoid this problem twin pull cable handlers have been developed and are currently used at many longwall operations, particularly in the USA, Australia and the UK. In a twin pull cable handler, each link defines a generally rectangular shaped box in which the electric cable and water line are located. The water hose is not kept separate from the electric cable as with the centre pull design. A removable plate or plates are bolted or otherwise fixed to the tops of the side walls of the rectangle, thereby locking the cables in the U shaped link. The base, side walls, and plate are all solid providing all round protection for the electric cable and water line. The links may be linked/pulled from either or both sides, and are typically pulled from both sides, hence the name “twin pull”. However, whilst such a twin pull design provides a high degree of protection for cables, it will be appreciated that it is an extremely lengthy, tedious and time consuming process to install a pair of lines in a twin pull cable handler compared to a centre pull cable handler such as in U.S. Pat. No. 4,988,838 or a side pull cable handler, because of the need to attach a plate to each link in turn. For a typical longwall mine which might require a cable handler which is many metres long, this may take many hours, even days, and will result in loss of operating time. There is also the risk of the bolts, clips or the like securing the plates to the channels, becoming loose and separating from the channel. It will also be appreciated that, because the links have to be articulated to allow the cable to fold back upon itself, as the coal cutter traverses up and down the coal face, however the cable handler is designed, it is impossible to totally enclose the cables In a cable handler which is made of articulated rigid protective elements, as gaps are required between links to allow articulation.
International Patent Application publication number WO 03/095797 discloses one attempted solution to this problem. The links of the cable handler disclosed in that publication define a channel having an end wall and flexible side walls for receiving at least one, and typically two service lines. Engaging formations are defined on the free ends of the side walls and a second end wall plate defining engaging formations adapted to engage with the engaging formations of the side wall is provided. Engagement between engaging formations is enabled by flexing of the side walls to securely engage the second end wall between the side arms thus preventing movement of the second end wall relative to the side walls, absent flexure of the side walls. At least one, and preferably both, of the end walls is provided with pivotal formations to enable the chain link to be pivotally connected to a similar link to form a chain. Although, in theory, the design of WO 03/095797 should provide good protection for cables against a the presence of stones, flints and like in the trough, in practice it has been found that the end wall plates are not securely retained in the line of maximum parting force between the side walls in all conditions, and the end wall could possibly disengage from the rest of the link, in use. Further in the design shown in WO 03/095797, the water hose is not kept separate from the electric cable.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.